Java8关闭流使用try with resource关闭资源的理解

try with resource是一个语法糖，可以使用该方式关闭流的前提是对象一定要实现AutoCloseable接口，其原理还是在编译的时候JDK给我们生成了finally来关闭流

源代码

public static String createImg(String message, int width, int height) {
    String img = "";
    ClassPathResource resource = new ClassPathResource("resources/font/SourceHanSansCN-Normal.ttf");
    try (ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
         InputStream fis = resource.getInputStream()){
        //创建画布
        BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //得到它的绘制环境(这张图片的笔)
        Graphics2D g2 = (Graphics2D) bi.getGraphics();
        //设置透明背景
        bi = g2.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);
        g2 = bi.createGraphics();
        Font font = java.awt.Font.createFont(java.awt.Font.TRUETYPE_FONT, fis);
        font = font.deriveFont(Font.PLAIN, 90);
        //设置字体:字体、字号、大小
        g2.setFont(font);
        //设置背景颜色
        g2.setColor(Color.red);
        int locY = g2.getFontMetrics().getHeight();
        drawString(g2, message, 0, locY, width - g2.getFontMetrics().charWidth(' '));
        // 输出png图片
        ImageIO.write(bi, "png", outputStream);
        img = Base64.encode(outputStream.toByteArray());
        g2.dispose();
    } catch (IOException | FontFormatException e) {
        e.printStackTrace();
    }
    return img;
}

反编译class的文件

public static String createImg(String message, int width, int height) {
    String img = "";
    ClassPathResource resource = new ClassPathResource("resources/font/SourceHanSansCN-Normal.ttf");

    try {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        Throwable var6 = null;

        try {
            InputStream fis = resource.getInputStream();
            Throwable var8 = null;

            try {
                BufferedImage bi = new BufferedImage(width, height, 1);
                Graphics2D g2 = (Graphics2D)bi.getGraphics();
                bi = g2.getDeviceConfiguration().createCompatibleImage(width, height, 3);
                g2 = bi.createGraphics();
                Font font = Font.createFont(0, fis);
                font = font.deriveFont(0, 90.0F);
                g2.setFont(font);
                g2.setColor(Color.red);
                int locY = g2.getFontMetrics().getHeight();
                drawString(g2, message, 0, locY, width - g2.getFontMetrics().charWidth(' '));
                ImageIO.write(bi, "png", outputStream);
                img = Base64.encode(outputStream.toByteArray());
                g2.dispose();
            } catch (Throwable var36) {
                var8 = var36;
                throw var36;
            } finally {
                if (fis != null) {
                    if (var8 != null) {
                        try {
                            fis.close();
                        } catch (Throwable var35) {
                            var8.addSuppressed(var35);
                        }
                    } else {
                        fis.close();
                    }
                }

            }
        } catch (Throwable var38) {
            var6 = var38;
            throw var38;
        } finally {
            if (outputStream != null) {
                if (var6 != null) {
                    try {
                        outputStream.close();
                    } catch (Throwable var34) {
                        var6.addSuppressed(var34);
                    }
                } else {
                    outputStream.close();
                }
            }

        }
    } catch (FontFormatException | IOException var40) {
        var40.printStackTrace();
    }

    return img;
}